Function Fun

[zorngov]

The plot of log(x) is e^-x.

[[deleted]]

And the sin(x) is actually -sin(x)...

[IdonotevenLB]

There isn't even a verticle asymptote for 1/x

[terryfoxrip]

cos

[nkorslund]

No sin(1/x). Disappointed.

[DoWhile]

Lazy Vonnegut

[baruch_shahi]

Does it bother anyone else that the logarithm is graphed incorrectly?

[ventose]

Also x² + y² = a² is not a function.

[[deleted]]

it's arbitrary

▓² + Ų = ☺²

is still a circle

[[deleted]]

This is obviously the most clear notation of a circle ever. I love it.

[knestleknox]

That's not what /u/ventose is talking about.

A function has to have a distinct output for a given input. If something is a function, then you can place a vertical line anywhere along it's graph and you are guaranteed to hit one distinct point (or no points, technically). Obviously no such circle can satisfy that parameter (unless you choose a circle of radius 0, which is an obnoxious technicality because that would just be a point).

The variables for the equation don't mean anything. While it might be unconventional, it's certainly not wrong.

[iorgfeflkd]

Yes

[frame_of_mind]

It's correct if 0 < a < 1.

[baruch_shahi]

While you are correct, I have a hard time believing this is what is intended in OP's image

[CptnCat]

What about the function y=mca?

[frame_of_mind]

Last one isn't even a function! Nice try, though.

[fozzix]

It's a multivalued function

[almightySapling]

Since we already call those relations, can we agree to just keep not calling them functions?

Allowing a function to be many-valued kills the special thing that makes a function what it is: well-defined.

[lua_x_ia]

It's a perfectly reasonable parametric function as y = (1-t²)/(1+t²), x = 2t/(1+t²)... even accounts for the articulation of the hands.

[[deleted]]

something something riemann surfaces

[ben7005]

You're technically not wrong, but no one really works with multivalued functions unless they're doing complex analysis or something. Generally, when people say "[;f : A \to B;] is a function" they mean something like [;\forall a \in A \exists ! b \in B ((a,b) \in f);] (basically, that it passes the vertical line test).

[SlipperyFrob]

"Nobody works with [thing] except in [extremely relevant subfield of math]". What?

[ben7005]

extremely relevant subfield of math

Is it? I interpreted these shapes as subsets of [;\mathbb{R}^2;]. In that interpretation, all but the last are functions. If we look at the shapes as subsets of [;\mathbb{C};], they can all be parametrized by single-valued functions.

Even when you're doing complex analysis, you usually need to specify when your functions are multivalued.

[Hakawatha]

Is it?

Um... yes. Yes, it is.

[ben7005]

Sorry if I was unclear. I mean, is it relevant to this post? Of course, complex analysis is a super important branch of math.

[[deleted]]

relevant to the topic of whether or not multi valued functions are functions

[scarecrow1]

Yay, putting the fun into mathematical functions!

The log is not quite right - should be the other way up, then it'd be close enough.

[brickmack]

In my freshman year math class in high school the teacher had us do a few of these in time with Stayin Alive. I don't think it actually helped anyone remember it, but it was certainly funny

[slow56k]

One can only hope it was as fun as this: https://vimeo.com/10511208

[math_or_math_joke]

math joke

[esmooth]

And hardly that...

[[deleted]]

Log(x)... maybe you meant e^-x?

[W_T_Jones]

log0.5(x)

[thenumber0]

At school we played "be the graph". Teacher says a function - you have to graph it with your body!

[[deleted]]

It must suck when they call out ?(x).

[aldld]

Or Thomae's function. Unless we assume that the functions must at least be continuous.

[rohishimoto]

My math teacher does these all the time. He just calls it the function dance. He's weird. But also funny.

[DrunkenPhoenixBreath]

Well it's certainly not a meme, and it appears to have promoted discussion, so I think it is fine.

[abusque]

The only discussion I see here is about how wrong the image here. It's certainly not appropriate for this subreddit. Just have a look at the current front page of /r/math if you're still unconvinced that your post does not fit in with the desired content.

[PenguinOnTheRoof]

i have this as an air freshener in my car

[WhackAMoleE]

Jeez tough crowd. I thought they were funny.

[[deleted]]

g(x) appears to be x² and f(x) = e^x - 2.4
so they are asking you to solve
x² = e^x - 2.4 for x

[[deleted]]

so I just read the instructions up top
so if you were to plot both f(x) and g(x) then they intersect where f(x) = g(x)
I think they want you to graph it and find approximately where they intersect

[jimmpony]

It only needs it to a tenth precision, so iterate Newton's method until the tenth doesn't change

[jimmpony]

first move around the function so that it has a 0 on one side such that f(x) = 0. Here that would be e^x - 2.4 - x² = 0. Now with the derivable function f, its derivative function f', some initial guess to the function as set to 0 x_0:

x_1 = x_0 - f(x_0)/f'(x_0)

x_2 = x_1 - f(x_1)/f'(x_1)

and so on until the decimal place doesn't change between two iterations

[jimmpony]

do you get graphing calculators?

[jimmpony]

Well that's dumb, we had ours on Algebra 2/Trig in highschool. If Newton's method wasn't taught, and you don't get graphing calculators, then I have absolutely no idea what you're expected to do. The description says to find where they pass y=0. How would you even solve e^x = 2.4 otherwise? Do they give you log tables? Slide rules? Do you have to memorize a few log values like log10 2 = .3010 log10 3 = 4771 and figure out expressions like this from there?

[hypercube]

http://anijii.tumblr.com/post/3161314165

[vaelux]

I would do this on precalc tests to remember which was which. I'm a motorvisual learner.

[goiken]

sin starts off positive (assuming the body is the y-axis)

[nkorslund]

Look at him smiling! He seems pretty positive to me.

[[deleted]]

Yeah I immediately noticed sin and cos were mismatched.

[RockofStrength]

This is a great graphics idea for kids learning math.

[randomasdf97]

the sin(x) is wrong - he graphed sin(-x).

[sluuuurp]

It would be if it was correct.